fix: reset s:is_wsl after calling (un)install

The behaviors of `firenvim#install` and `firenvim#uninstall` on WSL is
controlled by the script variable `s:is_wsl`: we initialize it to false
to (un)install firenvim on wsl side, and then set it to 1 to (un)install
on windows host side.

Currently, only `firenvim#install` and `firenvim#uninstall` changes the
value of `s:is_wsl`. The two function do not reset `s:is_wsl`, and thus
`s:is_wsl` is always 1 after calling them.

As a result, doing the followings sequentially in neovim have unexpected
results:

```lua
-- 1. `s:is_wsl` is set to 1
vim.fn["firenvim#install"](0)

-- 2. uninstall firenvim only on windows host because `s:is_wsl` is 1
vim.fn["firenvim#uninstall"]()
```

```lua
-- 1. `s:is_wsl` is set to 1
vim.fn["firenvim#uninstall"]()
-- 2. reinstall, installs scripts on host only, no scripts on WSL
vim.fn["firenvim#install"](0)
```

To fix this, a `try ... finally` block resets `s:is_wsl` even
if the two functions throw errors or run unsuccessfully.

autoload/firenvim.vim

@@ -895,6 +895,36 @@ function! firenvim#install(...) abort
  endif
  endif
 
+ try
+ if !s:is_wsl
+ call firenvim#internal_install(l:force_install, l:script_prolog)
+ let s:is_wsl = has('wsl') || !empty($WSL_DISTRO_NAME) || !empty ($WSL_INTEROP)
+ if s:is_wsl
+ echo 'Installation complete on the wsl side. Performing install on the windows side.'
+ call firenvim#internal_install(l:force_install, l:script_prolog)
+ endif
+ else
+ throw 'firenvim#install is called, but s:is_wsl has not been reset. Please report this bug.'
+ endif
+ finally
+ let s:is_wsl = v:false
+ endtry
+
+ if luaeval('lvim~=nil')
+ echo 'WARNING: Lunarvim is not supported. Do not open issues if you use Lunarvim.'
+ endif
+endfunction
+
+function! firenvim#internal_install(...) abort
+ let l:force_install = 0
+ let l:script_prolog = ''
+ if a:0 > 0
+ let l:force_install = a:1
+ if a:0 > 1
+ let l:script_prolog = a:2
+ endif
+ endif
+
  let l:execute_nvim_path = s:get_firenvim_script_path()
  let l:execute_nvim = s:get_executable_content(s:get_runtime_dir_path(), l:script_prolog)
 
@@ -978,18 +1008,6 @@ function! firenvim#install(...) abort
  echo 'Created registry key for ' . l:name . '.'
  endif
  endfor
-
- if !s:is_wsl
- let s:is_wsl = has('wsl') || !empty($WSL_DISTRO_NAME) || !empty ($WSL_INTEROP)
- if s:is_wsl
- echo 'Installation complete on the wsl side. Performing install on the windows side.'
- call firenvim#install(l:force_install, l:script_prolog)
- endif
- endif
-
- if luaeval('lvim~=nil')
- echo 'WARNING: Lunarvim is not supported. Do not open issues if you use Lunarvim.'
- endif
 endfunction
 
 " Removes files created by Firenvim during its installation process
@@ -1000,7 +1018,23 @@ endfunction
 " > Then, we set is_wsl to true if we're on wsl and launch
 " firenvim#uninstall again, uninstalling things on the host side.
 function! firenvim#uninstall() abort
+ try
+ if !s:is_wsl
+ call firenvim#internal_uninstall()
+ let s:is_wsl = has('wsl') || !empty($WSL_DISTRO_NAME) || !empty ($WSL_INTEROP)
+ if s:is_wsl
+ echo 'Uninstallation complete on the wsl side. Performing uninstall on the windows side.'
+ call firenvim#internal_uninstall()
+ endif
+ else
+ throw 'firenvim#uninstall is called, but s:is_wsl has not been reset. Please report this bug.'
+ endif
+ finally
+ let s:is_wsl = v:false
+ endtry
+endfunction
 
+function! firenvim#internal_uninstall() abort
  let l:data_dir = s:get_data_dir_path()
  call delete(l:data_dir, 'rf')
  echo 'Removed firenvim data directory.'
@@ -1052,14 +1086,6 @@ function! firenvim#uninstall() abort
  call delete(l:manifest_path)
  echo 'Removed native manifest for ' . l:name . '.'
  endfor
-
- if !s:is_wsl
- let s:is_wsl = has('wsl') || !empty($WSL_DISTRO_NAME) || !empty ($WSL_INTEROP)
- if s:is_wsl
- echo 'Uninstallation complete on the wsl side. Performing uninstall on the windows side.'
- call firenvim#uninstall()
- endif
- endif
 endfunction
 
 function! firenvim#onUIEnter(event) abort